Tire non-uniformity relates to the symmetry (or lack of symmetry) relative to the tire's axis of rotation in certain quantifiable characteristics of a tire. Conventional tire building methods unfortunately have many opportunities for producing non-uniformities in tires. During rotation of the tires, non-uniformities present in the tire structure produce periodically-varying forces at the wheel axis. Tire non-uniformities are important when these force variations are transmitted as noticeable vibrations to the vehicle and vehicle occupants. These forces are transmitted through the suspension of the vehicle and may be felt in the seats and steering wheel of the vehicle or transmitted as noise in the passenger compartment. The amount of vibration transmitted to the vehicle occupants has been categorized as the “ride comfort” or “comfort” of the tires.
Tire uniformity characteristics, or attributes, are generally categorized as dimensional or geometric variations (radial run out (RRO) and lateral run out (LRO)), mass variance, and rolling force variations (radial force variation, lateral force variation and tangential force variation, sometimes also called longitudinal or fore and aft force variation). Uniformity measurement machines often measure the above and other uniformity characteristics by measuring force at a number of points around a tire as the tire is rotated about its axis.
Once tire uniformity characteristics are identified, correction procedures may be able to account for some of the uniformities by making adjustments to the manufacturing process. Additional correction procedures can be performed to address non-uniformities of a cured tire including, but not limited to, the addition and/or removal of material to a cured tire and/or deformation of a cured tire.
Many different factors can contribute to the presence of non-uniformities in tires, including the presence of one or more product joints in the tire. Product joints are typically formed in various products during the manufacture of the tire, such as the casing textile plies, the belt plies, bead rings, the inner liner, the tread, and other rubber layers. The geometry of the joint coupled with the physical action of making the joint can have a significant impact on the uniformity of a tire.
Current methods of uniformity analysis can inaccurately separate continuous cyclic uniformity effects from more discrete effects, such as effects resulting from product joints, leading to reduced effectiveness of uniformity correction processes. The inaccuracies can occur in large part because discrete effects resulting from product joints are local phenomena similar to square wave and are not pure sinusoids. Such a joint shape will, in general, contribute to multiple uniformity harmonics simultaneously. Thus, correction procedures designed to address a uniformity problem at one harmonic can result in deterioration of uniformity at other harmonics.
Thus, a need exists for a system and method to more accurately identify the impact of discrete effects, such as effects resulting from product joints, on the uniformity of a tire.